The present invention relates generally to the treatment of process fluids and particularly, although not exclusively, the treatment of slurries comprising solids in liquids.
One technical field in which such slurries occur is in the treatment of organic material by bacteriological action, especially the so-called slurry digestion processes which are known for the treatment of organic waste materials.
One of the problems encountered in the treatment of process fluids both with bacteriological and other processes lies in the possibility of non-uniform treatment due to differences in the conditions encountered by the process fluid as it passes through the treatment system, and especially on differences in the residence time of the material within the system.
Where bacteriological action is involved, which frequently takes a relatively extended time period for completion, any material which follows a shorter than average route through the process material may be inadequately treated. This is unacceptable in the circumstances where the treatment processes is a biological breakdown of waste products because the resulting, partially-treated material may not be suitable for the uses to which the fully-treated material may be put. For example, biological breakdown of organic waste material such as animal excrement produces, when the treatment is complete, a residual solid material which is odour free and high in nutrients suitable for use as a horticultural or agricultural fertiliser. Inadequately treated material, on the other hand, may not be odour free, and more importantly may contain biological contaminants, pathogens or seeds the former of which could be dangerous or at least detrimental and the latter of which, if still viable may reduce the value of the material as a fertiliser.
Process fluids may also have constituents, such as salts or heavy metals the presence of which is unwanted or even dangerous. The present invention seeks, therefore, to provide apparatus for the treatment of process fluids in which means are provided by which the content of such unwanted components can be at least reduced.
The applicant""s own earlier British Patent Application GB-A-2 305 369 discusses apparatus for the treatment of process fluids of the general type having a vessel within which the process fluid is caused to circulate by the introduction of a stream of bubbles. By contrast Japanese publication JP-A-63295402 discloses a reactor at least part of the wall of which is formed with a hydrogen permselective membrane and an outer tube concentric with the reaction chamber.
According to the present invention there is provided treatment apparatus comprising a chamber for treatment of a process fluid and having at least two regions, means for causing the process fluid to follow a circulating path in each said region, the two regions communicating with one another such that process fluid introduced through an inlet into one region is constrained to flow into the other region before leaving the vessel, characterised in that at least part of the chamber wall in which an outlet is located is formed as a semi-permeable membrane contacted intimately by the process fluid following the said circulating path.
This allows for a selective transfer of material across the semi-permeable membrane, which may be made selective for those materials it is desired to remove. The circulating flow of the process fluid ensures that it comes into intimate contact with the semi-permeable membrane, especially in embodiments in which the outlet is located in an end wall such that the process fluid swirls around an outlet creating a vortex and causing the fluid to pass in close contact with the surface of the end wall. It is also possible for other walls to be formed entirely or partly as semi-permeable membranes, or even for all the walls defining the said chamber to be semi-permeable membranes. This is of particular relevance if the chamber is formed as a vessel immersed in a liquid bath or lagoon containing a liquid the composition of which encourages transfer of selected materials across the same semi-permeable membrane.
Embodiments of the invention may be made in which there are a plurality of chambers separated from one another by double-skinned partitions themselves defining compartments housing fluids co-operating in the transfer of selected materials across the semi-permeable membrane.
In one-embodiment of the invention a chamber for receiving a treatment fluid has a least two generally unobstructed interior regions in each of which the process fluid is caused to follow a circulating path, in which the means defining the overall paths of different parts of the process fluid between an inlet and an outlet to the chamber results in the path lengths being not substantially different for substantially all parts of the process fluid, and at least part of the chamber wall being formed as a semi-permeable membrane contacted by a process fluid in its circulating flow.
The inlet opening in the apparatus may open directly into one of the said two regions, and the outlet may correspondingly communicate with the other of the said two regions, the arrangement being such that process fluid introduced into the said one region through the inlet circulates in the said one region before transferring to the second region in which it circulates in contact with the semi-permeable membrane before leaving through the outlet.
Embodiments of the present invention may be formed as a treatment vessel for a process involving biological action on organic process materials comprising a solid/liquid, or liquid/liquid slurry or mixture, in which circulation, of the process material is driven by introducing gas at a low level within the vessel and allowing bubbles thereof to rise, with a collection region for solids from which solids can be extracted for further treatment.
In a preferred embodiment of the invention the bubble inlets are arranged in a plurality of rows thereof whereby to provide a xe2x80x9ccurtainxe2x80x9d of bubbles. In a vessel configuration such as that outlined above, in which the vessel has two regions in which the process fluid is caused to circulate in opposite directions, and in which the transfer of the process fluid from one to the other takes place in its transit through the vessel, the circulation-driving bubbles may form a xe2x80x9ccurtainxe2x80x9d between the two regions such that the process fluid must pass across the curtain of bubbles in its transit through the vessel. Any relatively dense particle of solid material entrained with the process fluid will, on passing through the bubble curtain, experience a significant reduction in its buoyancy thereby falling to the solids-collection region.
A configuration in which two rows of bubble inlets are provided may have a channel between the two rows of bubble inlets serving as this collection region, and such channel may house an auger or other means for driving the solid particles collecting therein towards a distribution point from which they can be removed from the vessel.
Removal of such solids from the vessel may involve the use of a water column within which the solids may be elevated, for example by means of a further auger or a gas lift apparatus, and which serves to maintain the gas tight closure of the vessel while nevertheless allowing solids to be extracted therefrom.
Regardless of the form of the vessels (and certain preferred configurations~will be described hereinafter in more detail) a treatment system for a process fluid may comprise a plurality of such vessels in sequence, so arranged that different processes take place in different vessels.
As an example, one embodiment of the present invention may comprise a treatment system for a process fluid comprising or including organic materials to be broken down by bacteriological action, comprising a plurality of chambers interconnected to receive the process fluid in sequence, each chamber having means for controlling at least one process parameter, and means for introducing fluid into the chamber in addition to the process fluid. There may further be provided means for directing process fluid from the outlet of a chamber to an inlet of the same chamber or to an inlet of another chamber upstream or downstream in relation to the flow of process fluid through the system.
The parameters which may be controlled within the chambers comprise the temperature of the process fluid within the chamber, the pressure within the chamber, the rate of flow of process fluid through the chamber, the precise bacteriological content of the chamber (in the case of biological processes, which may be achieved by introducing particular bacteria into it for inoculating the material therein) and/or the introduction or presence of other process reagents, in particular liquids or gases.
The introduction of a gas into the treatment vessel may be undertaken simply to drive the circulation of the process fluid within the vessel, in which case the gas may be chosen as one contributing to the maintenance of aerobic or anaerobic conditions as the case may require, or alternatively the gas may be one which takes part in the reaction proceeding within the vessel.
Whether the plurality of chambers are formed as compartments within a vessel by partitioning, or whether they are formed as separate vessels interconnected by ducting, it is preferred that at least some of the walls defining the chamber are in contact with a heat exchange fluid which can be driven in counter current with respect to the direction of flow of process fluid through the system. In this way, for example, exothermic reactions taking place in some of the chambers can be cooled by the heat exchange fluid and the heat transferred to other chambers whereby to raise the temperature of the material therein.